(634g) Programmable Morphogenesis Via the Directed Assembly of Colloid Structures

We have designed a method for the directed assembly of colloids (DACs), which is analogous to the preparation of peptide chains from monomeric units of amino acids. In this fashion, we have prepared colloidal ensembles that utilize colloids of different materials (as individual units) with linkages made from stable amide bonds. We fabricated 1 µm poly(N-isopropyl acrylamide-co-acrylic acid) (PNIPAAm-co-AA) particles that were pH and temperature responsive. pH-responsive poly(acrylic acid) particles were also prepared. Particles were synthesized via free radical precipitation polymerization. Janus particles, particles having a different chemical functionality on each face, were created via a pickering emulsion where aqueous exposed carboxylic acid moieties were converted to amine groups. Janus particles were also formed with carboxylic acid and thiol moieties, where amines were modified to thiol groups with N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) followed by reduction with dithiothreitol (DTT). Particles were bound to a gold substrate via the thiol anchor to initiate assembly of particles. 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) chemistry was used to form covalent amide bonds between carboxylic acid terminated and amine terminated particles. A stable chain was formed and removed from the Au surfaces. Rings could be formed by ending with a thiol-terminated janus particle. Synthesis of colloidal chains with pre-programmed sequences allows for the assembly of microstructures. These systems have been used to investigate global transformations by pH- and temperature-induced mechanical stresses. Different ratios of PNIPAAm-co-AA to pAA particles were used to form colloidosomes; upon expansion, buckling was observed. These programmable, responsive particle assemblies could be used to develop novel functional materials for tissue engineering.